Free-running atrial and demand ventricular pacer

ABSTRACT

An atrial and ventricular (bifocal) demand pacer. A device is disclosed for providing electrical stimulation to the atrium after a first pre-determined time, and to the ventricle after a second pre-determined time, where both pre-determined times are measured from the last natural heart-beat. The pacer monitors the ventricular endocardial electrogram and programs both the atrial and the ventricular stimulation accordingly. In patients with atrial bradycardia but normal AV conduction, only the atria are stimulated. When the condition is complicated with AV block, both the atria and the ventricles are pacer-controlled. The interval between the atrial and ventricular stimulation is selected to facilitate the proper atrio-ventricular timing sequence. The pacer does not compete with spontaneous ventricular contractions. A free-running atrial and ventricular demand pacer is disclosed for treating patients suffering from sinus arrest (no spontaneous atrial activity) concurrent with intermittent AV block.

United Stalks Patent 1191 11 3,709,229 1 1 Jan.9,1973

Berkovits [54] FREE-RUNNING ATRIAL AND DEMAND VENTRICULAR PACER [75] Inventor: Barough V. Berlrovits; Newton Highlands, Mass.

[73] Assignee: American Optical Southbridge, Mass.

Corporation,

[22] Filed: Feb. 9, 1971 21 Appl. 190.; 113,877

Related US. Application Data [63] Continuation-impart of Ser. No. 810,519, March 26,

1969, Pat. No. 3,595,242.

52 us. Cl. ..l28/419 P, 128/422 [51 1m. (:1. ..A6ln 1/34 [58] Field of Search ..128/419 P, 421,422

[56] References Cited UNITED STATES PATENTS 7 3,593,718 7/1971 Krasner "118/419 P 3,431,912 3/1969 Keller, .lr ..12s/419 P 3,557,796 1/1971 Keller, Jr. et al 128/419 P Primary ExaminerWilliam E. Kamrn Attorney-William C. Nealon, Noble S. Williams, Robert J. Bird and Joel Wall 57 ABSTRACT An atrial and ventricular (bifocal) demand pacer. A device is disclosed for providing electrical'stimulation to the atrium after a first pre-determined time, and to the ventricle after a second pre-determined time, where both pre-determined times are measured from the last natural heart-beat. The pacer monitors the ventricular endocardial electrogram and programs both the atrial and the ventricular stimulation accordingly. In patients with atrial bradycardia but normal AV conduction, only the atria are stimulated. When the condition is complicated with AV block, both the atria and the ventricles are pacer-controlled,

- The interval between the atrial and ventricular stimulation is selected to facilitate the proper atrio-ven tricular timing sequence. The pacer does not compete with spontaneous. ventricular contractions. A freerunning atrial and ventricular demand pacer is disclosed for treating patients suffering from sinus arrest (no spontaneous atrial activity) concurrent with intermittent AV block.

6 Claims, 5' Drawing Figures PATENTEDJMI 9 ms SHEET 1 UF 2 INVENTOR. BAROUH V. BERKOVITS PATENTEUJAH 9 ms SHEET 2 BF 2 mdE w vw

mdE

ouwzoow m uwwzoow INVENTOR. I BAROUH V. BERKOVITS FREE-RUNNING ATRIAL AND DEMAND VENTRICULAR PACER This patent application is a continuation in part of copending patent application, Ser. No. 810,519 filed on Mar. 26, 1969 and which was issued as U.S. Pat. No. 3,595,242 on July 27, 1971. The parent application is entitled Atrial and Ventricular Demand Pacer filed in the name of the applicant of the present invention.

This invention relates to pacers, and more particularly to demand pacers for use with patients exhibiting symptomatic atrial bradycardia and unpredictable AV block.

The electrical activity of a normal heart begins with a nerve impulse generated by a bundle of fibers located in the sinoatrial node. The impulse spreads across the two atria while they contract and speed the flow of blood into the ventricles underneath them. The atrial activity of the heart corresponds to the P wave in an electrocardiogram trace. The electrical impulse continues to spread across the atrioventricular (AV) node, which in turn stimulates the left and right ventricles. Typically, an interval of approximately 120-160 milliseconds elapses between atrial and ventricular stimulation. The ventricular activity corresponds to the QRS portion of the electrocardiogram, and typically has a duration of 80 milliseconds. Toward the end of each heartbeat, the ventricular muscles repolarize, and this portion of the electrical activity of the heart corresponds to the T wave in the electrocardiogram.

Of the two types of contractions, the ventricular is far more important than the atrial. The atrial contractions cause the ventricular contractions to be more efficient; the ventricular contractions are more effective if the ventricles are first filled with blood. While a patient can survive without proper atrial action, he cannot survive without ventricular contractions.

With an AV block, that is, an AV node which is open-circuited, life cannot be sustained (unless the ventricles somehow beat on their own without AV stimulation, and even in such a case the heartbeat rate is generally far too slow). With proper ventricular contractions, a patient can live even with atrial fibrillation. For this reason, early pacers-were generally used to protect against ventricular asystole. These pacers stimulated the ventricles continuously at a fixed rate to control their contractions.

Following the use of this type of pacer for many years, the demand pacer was introduced. in a demand pacer, electrical heart-stimulating impulses are provided only in the absence of natural heartbeats. If only a single natural heartbeat is absent, only a single electrical impulse is generated. If more than one natural heartbeat is missing, an equal number of electrical impulses will be provided. No matter how many electrical stimuli are generated, they occur at essentially the same time spacing from each other and from previous natural heartbeats as would be the case if they were all natural heartbeats. The result is an overall integrated" operation, i.e., a mutually exclusive cooperation of natural heartbeats and stimulating impulses. The demand pacemaker of this type is disclosed in my U.S. Pat. No. 3,345,990 issued on Oct. 10, 1967.

Generally, a demand pacer is-primed to generate an impulse at a predetermined time after the last natural heartbeat. If another natural heartbeat occurs during On the other hand, if a natural heartbeat does not take place by the end of time-out period a stimulating impulse is generated. For the proper operation of a demand pacer, the pacer circuitry must determine if a natural heartbeat has occurred. The largest magnitude electrical signal generated by the heart activity is the QRS complex corresponding to ventricular contraction. To determine whether a natural heartbeat has occurred, an electrode is generally coupled to a ventricle. Since in most cases ventricular stimulation is required, the same electrode can be used for both stimulating the ventricles and detecting a natural heartbeat, as disclosed in my aforesaid patent.

In the presence of noise, erroneous operation of a demand pacer. of this type can take place. The noise may result in the generation of an electrical signal on the ventricular electrode, and the pacemaker circuitry may treat this noise as indicative of a natural heartbeat and inhibit the generation of a stimulating impulse even if one is required. In my co-pending application, Ser. No. 727,129, filed on Apr. 11, 1968, which was issued on Sept. 15, 1970, as U.S. Pat. No. 3,528,428, an improved demand pacer is disclosed. In this improved demand pacer, in the presence of noise the pacer time-out period is not interrupted. Continuous stimulating impulses are generated, even if they are not required. It is better to provide an impulse even if it is not required than it is not to provide an impulse if it is required.

There are many patients with symptomatic atrial bradycardia even though they have normal AV conduction. In such a patient, the slow atrial rate causes the ventricular rate to slow down. Ventricular pacer stimulation has been used in the past to treat this disorder. For such patients, however, it would be better to provide atrial stimulation to thus control both the atrial and ventricular rates, with the additional benefit of the natural atrio-ventricular sequence. But such atrial stimulation would leave the patient unprotected from unpredictable AV block. Thus, provision should also be made for ventricular stimulation if it becomes necessary. 1

In certain patients suffering from what is termed sinus arrest, there are no impulses initiated in the sinus node and there is no spontaneous atrial activity. Therefore, these patients require treatment of this atrial condition, while at the same time, ventricular stimulation on demand should be used to protect against the possibility of AV block. The present invention provides this treatment by stimulating the atrium at a free-running rate while simultaneously stimulating the ventricle on demand.

These types of pacing could be accomplished wit the use of two individual pacers. But even if they are combined in a single package many problems must be overcome, especially if a demand-type operation is desired. One of the most obvious problems concerns the timing sequence of the two types of pacing.

It is a general object of my invention to provide a bifocal pacer for atrial as well as ventricular stimulation, which preferably is of the demand type.

It is a further object of my invention to provide a bifocal pacer for free-running atrial stimulation as well as ventricular demand stimulation.

In accordance with the principles of my invention the first function of the pacer is to generate an atrial stimulatingimpulse. After a predetermined time interval, the pacer functions to generate a ventricular stimulating impulse. Three electrodes are provided a neutral electrode, an electrode for atrial stimulation and an electrode for ventricular stimulation. In the illustrative embodiment of the invention, the ventricular electrode also serves to detect the occurrence of a ventricular contraction. I I

The pacer exhibits two time-out orescape intervals. Theventricular escape interval is 160-250 milliseconds longer than the atrial escape interval. The ventricular escape interval is greater than the normal interval between two heartbeats (as in a conventional demand pacer). The atrial escape interval is greater than the normal interval between atrial and ventricular beats (P,

to R), but less than the normal inter-beat interval (R to R). Both time-out periods begin with the generation of the last heartbeat (natural or stimulated). If another ventricular contraction does not occur within the atrial time-out period, that is, in the absence of a premature ventricular contraction, the atrial stimulating impulse is generated. The atria contract and fill the ventricles with blood. In the event the ventricles contract (i.e., there is no AV block), the detected ECG signal on the ventricular electrodes resets both time-out circuits and the ventricular impulse is not, generated. In the event the contraction does not occur, a ventricular impulse is generated at the end of the ventricular time-out interval.

FIG. 1 is the same as FIG. I in US. Pat. No.

3,528,428 and depicts a preferred demand pacer for ventricular stimulation, and further shows in heavy lines the additional circuit elements and the five conductors 80-84 which are required to connect the demand pacer of FIG. 1 to the atrial stimulating circuit of FIG. 3;

FIG. 2 depicts a typical electrocardiogram;

FIG. 3 depicts an trial stimulating circuit which, when used with the circuit of FIG. 1, provides bifocal stimulation in accordance with the preferred embodiment of the present invention;

FIG. 4 depicts the arrangement of FIGS. 1 and 3; and

FIG. 5' is a timing diagram which will be helpful in understanding the present invention.

Except for the elements and conductors shown in heavy lines, the circuit of FIG. I is identical to that disclosed in U.'S. Pat. No. 3,528,428. (In said application, conductor 11 extends directly from electrode E1 to capacitor 17 there is no FET switch 92 in the signal path.) Electrodes El and E2 are implanted in the patients heart, electrode E2 being the neutral electrode and electrode El being positioned to stimulate the ventricles of the patients heart. When switch S is'closed, the pacer functions to continuously supply electrical impulses at a fixed rate. When the pacer is operated in the demand mode, however, switch S is open. Current flows-between electrodes E1 and E2 to stimulate the ventricles only when an electrical stimulus is required.

Capacitor serves to provide a source of current when an impulse is required. At that time, transistor T9 conducts and the capacitor discharges through the electrodes. Capacitor 57 charges through potentiometer 35 and 37 until the voltage across it causes transistors T7 and T8 to conduct. At that time, capacitor 57 discharges through transistors T7 and T8, transistor T9 conducts, and an impulse is delivered to the patients heart from capacitor 65. The setting of potentiometer 37 controls the time taken for capacitor 57 to discharge, that is, the width of each impulse. The. setting of potentiometer 35 controls the time required for capacitor 57 to charge to that level which causes conduction in transistors T7 and T8, that is, the interpulse interval. Ordinarily, in the absence of conduction of transistor T6, capacitor 57 would continuouslycharge and discharge, and impulses would be supplied to the patients heart at-fixed intervals determined by the setting of potentiometer 35.

Electrode E1 is coupled over conductor 11 to the base of transistor T1. A typical ECG trace is shown in FIG. 2, and transistors T1 and T2 conduct when electrode El detects a ventricular contraction which results in the generation of an R wave. (Excessive signals are shorted through Zener diode 67 to prevent damage to transistor T1.) With the conduction of these transistors, a positive pulse is delivered to the base of transistor T6. Transistor T6 conducts and capacitor 57 discharges through it. Thus, although the'capacitorwas previously charging to the level which would have resulted in the generation of an impulse, it is discharged and a new time-out interval begins. This arrangement ensures that an impulse is not generated if a natural I heartbeat has occurred. The time-out interval is such that impulses are generated with an inter-pulse interval slightly in excess of the desired natural inter-beat interval. Only if a natural heartbeat is missing is a stimulating impulse generated.

The remaining transistors in the circuit serve to prevent conduction of transistor T6 in the presence of noise. In the presence of noise it would otherwise be possible for transistor T6 to conduct and prevent the generation of an impulse even though one is required. For this reason, when the pacer detects extraneous noise, transistor T6 is prevented from operating and impulses are delivered at a fixed rate. A more complete description of the operation of the circuit of 'FIG. 1 is set forth in my above-identified application.

The illustrative embodiment of the invention is derived by adding the circuit elements and, conductors shown in'heavy lines in FIG. 1, and combining the circuits of FIGS. 1 and 3, as shown in FIG. 4. The circuit of FIG. 3 is in almost all respects identical to the. circuitry on the right side of FIG. 1. The various elements in the circuit of FIG. 3 are designated by the same numerals as the equivalent elements in FIG. 1 with the addition of prime symbols. Conductor couples potentiometer 35' and resistor 59 to a terminal of battery 7 just as potentiometer 35 and resistor 59 are coupled to the same terminal in FIG. 1. Conductor 81 couples the base of transistor T7 to the other terminal of battery 7 just as the base of transistor T7 in FIG. 1 is coupled to this terminal. Conductor 82 couples the base of transistor T6 to the right side of capacitor 53, just as the base of transistor T6 in FIG. 1 is coupled to theright side of the capacitor. Conductor 83 serves to provide a common neutral for the circuits of FIGS. 1 and 3. Finally, conductor 84 serves to extend a signal to disable FET switch 92, as will be described below.

Electrode E3 in FIG. 3 is implanted in the patinets heart to stimulate his atria. The circuit of FIG. 3 functions just as does the circuit on the right side of FIG. 1, except that each stimulating impulse results in an atrial contraction rather than a ventricular contraction. Capacitor 57' charges through potentiometers 35 and 37'. After a predetermined interval, when the capacitor voltage has reached the level required to control conduction of transistors T7 and T8 the two transistors conduct and forward bias the base-emitter junction of transistor T9. The charge on capacitor 65 flows through transistor T9 and electrodes E2 and E3. The width of each pulse is determined by the setting of potentiometer 37 which determines the time required for capacitor 57' to discharge through transistors T7 and T8. The inter-pulse interval is determined by the setting of potentiometer 35 which determines the time required for capacitor 57' to charge to the level which causes transistors T7- and T8 to conduct. 7 Any pulse delivered through capacitor 53 as a result of the detection of an R wave causes transistor T6 to conduct along with transistor T6. At the same time that capacitor 57 discharges through transistor T6, capacitor 56 discharges through transistors T6. In such an event, the time-out period of the circuit of FIG. 3 is not concluded and an atrial stimulating pulse is not generated. Instead, the time-out begins once again.

FIG. 5 depicts a timing sequence which will be helpful in understanding the present invention. Two R waves are shown and represent two successive beats (ventricular contractions) of the patients heart. Typically, the time interval between them is less than 760 milliseconds. The P wave associated with the second R wave is shown occuring before it.

Potentiometer 35' has a value such that capacitor 57' charges to the level required for the conduction of transistors T7 and T8 after 600 milliseconds have elapsed since the last capacitor discharge. The atrial stimulating pulse E3 is thus shown occuring 600 milliseconds after the first R wave. It should be noted that the atria are stimulated following the P wave during a generated following the atrial contraction, that is, during the refractory interval of the atria, it has no effect on the beating 1 action of the patients heart. (The generation of an atrial stimulating impulse prior to the natural atrial contraction can induce an atrial premature beat which is not desirable.)

Potentiometer 35 in FIG. 1 has a value such that the time-out interval for the ventricular stimulation is 800 milliseconds. Thus, the pulse designated E1 in FIG. 5 is shown occuring 800 milliseconds after the first R wave, which is slightly after the second R wave should it be present. If the second R wave is detected on electrode El, both time-out circuits are reset and an impulse is not generated on electrode El. This is the desired devmand-type operation. If a natural heartbeat does not occur within 800 milliseconds after the last heartbeat,

6 an impulse is generated on electrode E1 to stimulate the ventricular contraction.

It should be noted that if the heart beats naturally, there will be no ventricular stimulation by the pacer. However, there will be atrial stimulation because the 600 millisecond time-out interval of the circuit of FIG. 3 is less than the natural interpulse interval. But in the event a natural atrial contraction does not take place, the atrial stimulation is required in order that the heart functions more efficiently. The ventricular stimulation, of course, is provided to correct any AV block. A normal ventricular contraction can occur approximately 120-160 milliseconds after the atrial stimulation. The ventricular time-out period in the circuit of FIG. 3 is 200 milliseconds longer than the atrial time-out period in the circuit of FIG. 1; sufficient time is allowed for a natural ventricular contraction before a ventricular stimulating impulse is generated. In general, the ventricular time-out period should exceed the atrial timeout period by 160-250 milliseconds.

It should also be noted that the operation of the circuit of FIG. 3 is keyed to the detection of a ventricular contraetionby the circuit of FIG. 1. It is highly desirable to key the circuit of FIG. 3 to the beating of the patients heart were a free-running generator provided to stimulate the atria, the timing of the beating of the patients heart might be seriously affected. (However,

in sinus arrest, the atrium does not beat spontaneously,

and timing is not a problem.) While the natural timing change, the circuitry timing would be invarianL For this reason, capacitor 57' is discharged following any beating of the patients heart. Theoretically, it might be possible to detect an atrial contraction, that is,'to detect the P wave, and to discharge capacitor 57 before its time-out is completed so that aniatrial stimulating impulse would not be generated if it is not required. However, it is exceedingly difficult to detect the F wave due to its small magnitude as compared to the R wave. For this reason, in the illustrative embodiment of the invention it is the detection of the R wave which also serves to reset the time-out period of the circuit of FIG. 3. Of course, this results in the continuous generation of impulses at electrode E3 if the heart is beating normally (even though impulses at electrode El are not generated) because each R wave is detected after the impulse at electrode E3 has been generated. However, the generation of an atrial stimulating impulse during the refractory interval of the atria has been found not to interfere with the normal beating of a patients heart. (The same is not true of the generation of a ventricular stimulating impulse following a ventricular contraction, and this is the reason for the use of the demand-type pacers in the first place.)

It is possible in some cases that the atrial contraction will generate an electrical signal on electrode E1 which will cause transistor T1 to conductand re-start the two time-out periods. For this reason, FET switch 92 is inserted in conductor 11 between electrode El and capacitor 17 in the base circuit of transistor T1. The switch is normally conducting due to its connection through resistor 94 to neutral conductor 9. The negative pulse generated at electrode E3 is transmitted over conductor 84 and through diode 95 to capacitor 93.

The'capacitor chargesarid turns of? the FET switch. When the atrial stimulating pulse terminates (after a typical duration of 2 milliseconds), capacitor 93 discharges through resistor 94. The time constant of the capacitor-resistor combination is such that the FET switch remains off for approximately an'additional 6 milliseconds to prevent erroneous detection of a ventricular contraction for a few additional milliseconds until after all transients have died down. In this manner, the heartbeat detection circuit is disabled during each atrial stimulation and for a short interval thereafter. Capacitor 91 is provided tov short high frequency transients, arising from the FET switching, to conductor 9.

The time-out intervals of 600 milliseconds and 800 milliseconds shown in FIG. 5 are not critical. Considerable flexibility is possible. Generally, the time-out interval for the circuit of FIG. 3 should be such that an impulse is generated at electrode E3 some time between the P and R waves following a previous R wave. The time-out interval for the circuit of FIG. 1 should be such that an impulse is generated at electrode El at a time after the last R wave which exceeds the desired period between natural heartbeats;

The above circuitry is modified to provide freerunning atrial stimulation in which the atrial stimulator (depicted in FIG. 3) is not reset uponthe occurrence of a detected natural heartbeat (but where the ventricular stimulator is reset upon the occurrence of the detected natural heartbeat). This arrangement is useful in treating a patient suffering from sinus arrest during which there is no spontaneous atrial activity.

This circuit modification can readily be made by removing conductor 82 which connects the two bases of transistors T6 and T6. Thus, transistor T6 is still rendered conductive upon occurrence of a detected natural heartbeat and still discharges capacitor 57 prior to its causing a ventricular stimulation pulse to be generated. But, because of the removal of conductor 82, there will be no conduction of transistor T6 due to that occurrence of the detected natural heartbeat and capacitor 57' is not discharged prior to its causing an atrial stimulation. In addition, transistor T6 and resistor 55 can be removed from the circuit if desired.

Capacitor 57 in conjunction with potentiometers 35' and 37' and transistors T7 and T8 form a relaxation oscillator. The oscillator frequency can be selected to be greater than, equal to, or less than the ventricular demand frequency by the choice of component values. This oscillator causes free-running atrial stimulation.

It is thus seen that the pacer of the invention serves to correct for the condition known as atrial bradycardia at the same time that it protects against ventricular asystole. Although the invention has been described with reference to particular embodiments, it is to be understood that they are merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.

What is claim is:

l. A pacer comprising terminal means for connection to a patients heart for atrial stimulation, terminal means for connection to said patients heart for ventricular stimulation, a first timing circuit including first, free-running means for generating an electrical impulse on said atrial terminal means, a second timing circuit including second means for generating an electrical impulse on said ventricular terminal means, means for detecting a beating action of said. patients heart, and

means responsive to the operation of said detecting means for resetting said second timing'circuit.

2. A pacer in accordance with claim 1 wherein said detecting means includes other means for detecting a ventricular contraction of said patients heart.

3. A pacer in accordance with claim I wherein the period of said first timing circuit is shorter than the normal interval between two successive R waves in the electrocardiographic waveform of said patient.

4. A pacer in accordance with claim 1 wherein the period of said second timing circuit is longer than the normal interval between successive R waves in the electrocardiographic waveform of said patient.

5. A pacer in accordance with claim 1 further including means forpreventing the resetting of said second timing circuit responsiveto the operation of said detecting means in the presence of noise which would be confused with a beating action of said patients heart.

6. A pacer in accordance with claim 1 wherein said atrial and ventricular terminal means together include only three electrodes. 

1. A pacer comprising terminal means for connection to a patient''s heart for atrial stimulation, terminal means for connection to said patient''s heart for ventricular stimulation, a first timing circuit including first, free-running means for generating an electrical impulse on said atrial terminal means, a second timing circuit including second means for generating an electrical impulse on said ventricular terminal means, means for detecting a beating action of said patient''s heart, and means responsive to the operation of said detecting means for resetting said second timing circuit.
 2. A pacer in accordance with claim 1 wherein said detecting means includes other means for detecting a ventricular contraction of said patient''s heart.
 3. A pacer in accordance with claim 1 wherein the period of said first timing circuit is shorter than the normal interval between two successive R waves in the electrocardiographic waveform of said patient.
 4. A pacer in accordance with claim 1 wherein the period of said second timing circuit is longer than the normal interval between successive R waves in the electrocardiographic waveform of said patient.
 5. A pacer in accordance with claim 1 further including means for preventing the resetting of said second timing circuit responsive to the operation of said detecting means in the presence of noise which would be confused with a beating action of said patient''s heart.
 6. A pacer in accordance with claim 1 wherein said atrial and ventricular terminal means together include only three electrodes. 